1. Field of the Invention
The present invention relates to an apparatus for controlling the rotational speed of an electrically operated radiator fan in an internal combustion engine.
2. Description of the Related Art
In an electrically operated radiator fan device, the radiator fan is connected to an electric drive apparatus. The apparatus includes a first electric motor for a large electric current and a second electric motor for a small electric current. These first and second electric motors are selectively or simultaneously operated in accordance with the engine cooling requirements, such as the engine cooling water temperature or the condition of the air conditioner, to attain a desired fan speed which is sufficient to properly cool the radiator.
In this system, the large electric current motor and the small electric current motor are intended to operate sequentially in accordance with an increase in engine temperature. When the engine is started, the low electric current motor is first operated, since the engine temperature at that time is usually low. As a result of an increase in the engine cooling water temperature after the engine has been started, the large electric current motor is then operated. However, in a particular situation, conditions may arise wherein the small and large electric current motors should be simultaneously operated when the engine is started. In this case, a large rush current is generated in an electric circuit to operate relays for controlling the small and large electric current motors when the engine ignition switch is made ON to start the engine. This has an adverse effect on parts of the relays, such as the coils and contacts, from the viewpoint of a prolonged reliable service life thereof. To avoid this difficulty, it is easily conceivable to increase the electric capacity of these parts, but this is disadvantageous from the viewpoint of cost, and the need for the dimensions of the parts to be increased, which causes difficulties in the mounting of the device in a restricted space in the vehicle.